Localized heating techniques incorporating tunable infrared element(s) for vacuum insulating glass units, and/or apparatuses for same

ABSTRACT

Certain example embodiments of this invention relate to edge sealing techniques for vacuum insulating glass (VIG) units. More particularly, certain example embodiments relate to techniques for providing localized heating to edge seals of units, and/or unitized ovens for accomplishing the same. In certain example embodiments, infrared (IR) heating elements are controllable to emit IR radiation at a peak wavelength in the near infrared (NIR) and/or short wave infrared (SWIR) band(s), and the peak wavelength may be varied by adjusting the voltage applied to the IR heating elements. The peak wavelength may be selected so as to preferentially heat the frit material used to form a VIG edge seal while reducing the amount of heat provided to substrates of the VIG unit. In certain example embodiments, the substrates of the VIG unit do not reach a temperature of 325 degrees C. for more than 1 minute.

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to edge sealingtechniques for vacuum insulating glass (VIG) units. More particularly,certain example embodiments relate to techniques for providing localizedheating to edge seals of units, and/or unitized ovens for accomplishingthe same. In certain example embodiments, a plurality of infrared (IR)heating elements are controllable to emit IR radiation at a peakwavelength in the near infrared (NIR) and/or short wave infrared (SWIR)band(s), and the peak wavelength may be varied by adjusting the voltageapplied to the IR heating elements. The peak wavelength may be selectedso as to preferentially heat the frit material used to form a VIG edgeseal while reducing the amount of heat provided to substrates of the VIGunit.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Vacuum IG units are known in the art. For example, see U.S. Pat. Nos.5,664,395, 5,657,607, and 5,902,652, the disclosures of which are allhereby incorporated herein by reference.

FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit orVIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2and 3, which enclose an evacuated or low pressure space 6 therebetween.Glass sheets/substrates 2 and 3 are interconnected by peripheral or edgeseal of fused solder glass 4 and an array of support pillars or spacers5.

Pump out tube 8 is hermetically sealed by solder glass 9 to an apertureor hole 10 which passes from an interior surface of glass sheet 2 to thebottom of recess 11 in the exterior face of sheet 2. A vacuum isattached to pump out tube 8 so that the interior cavity betweensubstrates 2 and 3 can be evacuated to create a low pressure area orspace 6. After evacuation, tube 8 is melted to seal the vacuum. Recess11 retains sealed tube 8. Optionally, a chemical getter 12 may beincluded within recess 13.

Conventional vacuum IG units, with their fused solder glass peripheralseals 4, have been manufactured as follows. Glass frit in a solution(ultimately to form solder glass edge seal 4) is initially depositedaround the periphery of substrate 2. The other substrate 3 is broughtdown over top of substrate 2 so as to sandwich spacers 5 and the glassfrit/solution therebetween. The entire assembly including sheets 2, 3,the spacers, and the seal material is then heated to a temperature ofapproximately 500° C., at which point the glass frit melts, wets thesurfaces of the glass sheets 2, 3, and ultimately forms hermeticperipheral or edge seal 4. This approximately 500° C. temperature ismaintained for from about one to eight hours. After formation of theperipheral/edge seal 4 and the seal around tube 8, the assembly iscooled to room temperature. It is noted that column 2 of U.S. Pat. No.5,664,395 states that a conventional vacuum IG processing temperature isapproximately 500° C. for one hour. Inventor Collins of the '395 patentstates in “Thermal Outgassing of Vacuum Glazing,” by Lenzen, Turner andCollins, that “the edge seal process is currently quite slow: typicallythe temperature of the sample is increased at 200° C. per hour, and heldfor one hour at a constant value ranging from 430° C. and 530° C.depending on the solder glass composition.” After formation of edge seal4, a vacuum is drawn via the tube to form low pressure space 6.

Unfortunately, the aforesaid high temperatures and long heating times ofthe entire assembly utilized in the formulation of edge seal 4 areundesirable, especially when it is desired to use a heat strengthened ortempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown inFIGS. 3-4, tempered glass loses temper strength upon exposure to hightemperatures as a function of heating time. Moreover, such highprocessing temperatures may adversely affect certain low-E coating(s)that may be applied to one or both of the glass substrates in certaininstances.

FIG. 3 is a graph illustrating how fully thermally tempered plate glassloses original temper upon exposure to different temperatures fordifferent periods of time, where the original center tension stress is3,200 MU per inch. The x-axis in FIG. 3 is exponentially representativeof time in hours (from 1 to 1,000 hours), while the y-axis is indicativeof the percentage of original temper strength remaining after heatexposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis inFIG. 4 extends from zero to one hour exponentially.

Seven different curves are illustrated in FIG. 3, each indicative of adifferent temperature exposure in degrees Fahrenheit (° F.). Thedifferent curves/lines are 400° F. (across the top of the FIG. 3 graph),500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottomcurve of the FIG. 3 graph). A temperature of 900° F. is equivalent toapproximately 482° C., which is within the range utilized for formingthe aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2.Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled byreference number 18. As shown, only 20% of the original temper strengthremains after one hour at this temperature (900° F. or 482° C.). Such asignificant loss (i.e., 80% loss) of temper strength is of courseundesirable.

In FIGS. 3-4, it is noted that much better temper strength remains in athermally tempered sheet when it is heated to a temperature of 800° F.(about 428° C.) for one hour as opposed to 900° F. for one hour. Such aglass sheet retains about 70% of its original temper strength after onehour at 800° F., which is significantly better than the less than 20%when at 900° F. for the same period of time.

Another advantage associated with not heating up the entire unit for toolong is that lower temperature pillar materials may then be used. Thismay or may not be desirable in some instances.

Even when non-tempered glass substrates are used, the high temperaturesapplied to the entire VIG assembly may melt the glass or introducestresses. These stresses may increase the likelihood of deformation ofthe glass and/or breakage.

Thus, it will be appreciated that there is a need in the art for avacuum IG unit, and corresponding method of making the same, where astructurally sound hermetic edge seal may be provided between opposingglass sheets. There also exists a need in the art for a vacuum IG unitincluding tempered glass sheets, wherein the peripheral seal is formedsuch that the glass sheets retain more of their original temper strengththan with a conventional vacuum IG manufacturing technique where theentire unit is heated in order to form a solder glass edge seal.

An aspect of certain example embodiments of this invention relates toapplying localized heating to the periphery of a unit to form edge sealsto reduce the heating of the non-peripheral areas of the unit andthereby reduce the chances of the substrates breaking.

An aspect of certain example embodiments relates to providing stagedheating, localized heating, and staged cooling of a unit via a unitizedoven, the localized heating being provided by a substantially linearfocused infrared (IR) heat source comprising an array or matrix oflinear heat sources.

Another aspect of certain example embodiments relates to providing avacuum IG unit having a peripheral or edge seal formed so that at leastcertain portion(s) of thermally tempered glass substrates/sheets of thevacuum IG unit retain more of their original temper strength than ifconventional edge seal forming techniques were used with the solderglass edge seal material.

Another aspect of certain example embodiments relates to providing avacuum IG unit, and method of making the same, wherein at least aportion of the resulting thermally tempered glass substrate(s) retain(s)at least about 50% of original temper strength after formation of theedge seal (e.g., solder glass edge seal).

Another aspect of certain example embodiments relates to reducing theamount of post-tempering heating time necessary to form aperipheral/edge seal in a vacuum IG unit.

In certain example embodiments of this invention, an apparatus forforming an edge seal in a vacuum insulated glass (VIG) unit is provided.A plurality of infrared (IR) heating elements are controllable to emitIR radiation at a peak wavelength in the near infrared (NIR) and/orshort wave infrared (SWIR) band(s). The IR heating elements are spacedapart from one another so as to have a 2-6″ center-to-center distance.The IR heating elements are vertically positioned 1-36″ (more preferably2-10″) above an upper surface and/or below a lower surface of a VIGsubassembly insertable therein. A controller is operable to adjust anamount of voltage supplied to the plurality of IR heating elements tovary the peak wavelength produced by the plurality of IR heatingelements. Inner walls of the apparatus comprise a material havingcharacteristics suitable for causing a reduced amount of IR radiationfrom the IR heating elements impinging thereon to be reflected, with thereflected IR radiation being reflected in a generally diffuse orundirected pattern. Insulation is provided around the inner walls.

In certain example embodiments of this invention, a method of making avacuum insulated glass (VIG) unit comprising an edge seal is provided. AVIG subassembly is inserted into an apparatus including a plurality ofinfrared (IR) heating elements controllable to emit IR radiation at apeak wavelength in the near infrared (NIR) and/or short wave infrared(SWIR) band(s), with the plurality of IR heating elements being spacedapart from one another so as to have a 2-6″ center-to-center distanceand being vertically positioned 2-10″ above an upper surface and/orbelow a lower surface of the VIG subassembly. Inner walls of theapparatus comprise a material having characteristics suitable forcausing a reduced amount of IR radiation from the IR heating elementsimpinging thereon to be reflected, with the reflect IR radiation beingreflected in a diffuse or undirected pattern. Insulation is providedaround the inner walls. Frit material provided around the periphery ofthe VIG subassembly is heated via the plurality of IR heating elementsin forming the edge seal, with the amount of voltage being supplied tothe plurality of IR heating elements being adjustable to vary the peakwavelength produced by the plurality of IR heating elements so as topreferentially heat the frit material compared to glass substrates ofthe VIG subassembly.

In certain example embodiments of this invention, an apparatus forforming an edge seal in a vacuum insulated glass (VIG) unit is provided.A plurality of infrared (IR) heating elements are controllable to emitIR radiation at a peak wavelength in the near infrared (NIR) and/orshort wave infrared (SWIR) band(s). A controller is operable to adjustan amount of voltage supplied to the plurality of IR heating elements tovary the peak wavelength produced by the plurality of IR heatingelements. The controller is operable in first and second modes, with thefirst mode being a preheat mode at which the IR heating elements operateat approximately half power density and 25-75% (more preferably 45-55%)voltage and with the second mode being a frit sealing mode at which theIR heating elements operate at a half power density and at 50-100% (morepreferably 75-85%) voltage.

In certain example embodiments of this invention, a method of making aVIG unit is provided. A VIG subassembly is provided to a heater, withthe VIG subassembly comprising first and second substantially parallelspaced apart glass substrates, a plurality of support pillars betweenthe first and second glass substrates, and a frit material for formingan edge seal therebetween. Infrared (IR) energy is emitted from at leastone bulb operating at approximately half power density so as to preheatthe VIG subassembly. IR energy is emitted from the at least one bulboperating at approximately half power density and at a pre-selected peakIR wavelength at which the first and second glass substrates have anabsorption of less than 30% and at which the frit material has anabsorption of greater than 50% (more preferably greater than 70% or 80%)in making the VIG unit.

The features, aspects, advantages, and example embodiments describedherein may be combined to realize yet further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is a prior art cross-sectional view of a conventional vacuum IGunit;

FIG. 2 is a prior art top plan view of the bottom substrate, edge seal,and spacers of the FIG. 1 vacuum IG unit taken along the section lineillustrated in FIG. 1;

FIG. 3 is a graph correlating time (hours) versus percent temperingstrength remaining, illustrating the loss of original temper strengthfor a thermally tempered sheet of glass after exposure to differenttemperatures for different periods of time;

FIG. 4 is a graph correlating time versus percent tempering strengthremaining similar to that of FIG. 3, except that a smaller time periodis provided on the x-axis;

FIG. 5 is a simplified side view illustrating an example layout of afive chamber oven in accordance with an example embodiment;

FIG. 6 is an overhead view of the moving concentration of IR heatsources in the edge sealing zone of a unitized oven in accordance withan example embodiment;

FIG. 7 is a side view of a concentration and/or focusing mirror locatedproximate to an IR heating element in accordance with an exampleembodiment;

FIG. 8 is an illustrative flowchart showing a process for providinglocalized heating to frit edge seals of a VIG assembly via a unitizedoven, in accordance with an example embodiment; and

FIG. 9a is an overhead view of the VIG assembly on a belt in an ovenprior to its entry under the IR source array, in accordance with anexample embodiment;

FIG. 9b is an overhead view of the VIG assembly on a belt in an ovenentering into the IR source array, in accordance with an exampleembodiment;

FIG. 9c is an overhead view of the VIG assembly further entering the IRsource array such that both the edge to be sealed along the minor axisof the VIG assembly and portions of the edges to be sealed along themajor axis of the VIG assembly are both exposed to IR from the IR sourcearray, in accordance with an example embodiment;

FIG. 9d is an overview of the VIG assembly further entering the IRsource array such that only the edges to be sealed along the major axisof the VIG assembly are exposed to IR from the IR source array, inaccordance with an example embodiment;

FIG. 9e is an overhead view of the VIG assembly exiting the IR sourcearray, in accordance with an example embodiment;

FIG. 9f is an overhead view of a second VIG assembly entering the IRsource array as a first VIG assembly exits the IR source array inaccordance with an example embodiment;

FIG. 10 is an overhead view of an IR source array incorporating astaggered IR heat source design, in accordance with an exampleembodiment;

FIG. 11a is a side view of an in-line style belt furnace installed withan array of IR sources in accordance with an example embodiment;

FIG. 11b is a side view of an in-line style belt furnace installed withtwo arrays of IR sources in accordance with an example embodiment;

FIG. 12 is a graph that plots transmission, reflection, and absorptionvs. wavelength for an example glass frit;

FIG. 13 is a graph showing glass absorption vs. wavelength for 3.2 mmclear float glass;

FIG. 14 correlates voltage with temperature for example IR heatingelements;

FIG. 15 is a graph with absorption properties of a frit materialaccording to certain example embodiments;

FIGS. 16a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 40% voltage, full bulb (100% bulb usage)trial;

FIGS. 17a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 50% voltage, full bulb (100% bulb usage)trial;

FIGS. 18a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 60% voltage, full bulb (100% bulb usage)trial;

FIGS. 19a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 50% voltage, half bulb (50% bulb usage)trial;

FIGS. 20a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 60% voltage, half bulb (50% bulb usage)trial;

FIGS. 21a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 70% voltage, half bulb (50% bulb usage)trial;

FIGS. 22a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 80% voltage, half bulb (50% bulb usage)trial; and

FIGS. 23a-b are graphs that plot temperature vs. time for top and bottomlocations, respectively, for a 90% voltage, half bulb (50% bulb usage)trial.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Certain embodiments of this invention relate to an improved peripheralor edge seal in a vacuum IG window unit, and/or a method of making thesame. “Peripheral” and “edge” seals herein do not mean that the sealsare located at the absolute periphery or edge of the unit, but insteadmean that the seal is at least partially located at or near (e.g.,within about two inches) an edge of at least one substrate of the unit.Likewise, “edge” as used herein is not limited to the absolute edge of aglass substrate but also may include an area at or near (e.g., withinabout two inches) of an absolute edge of the substrate(s). Also, it willbe appreciated that as used herein the term “VIG assembly” refers to anintermediate product prior to the VIG's edges being sealed andevacuation of the recess including, for example, two parallel-spacedapart substrates and a frit. Also, while the frit may be said to be “on”or “supported” by one or more of the substrates herein, this does notmean that the frit must directly contact the substrate(s). In otherwords, the word “on” covers both directly and indirectly on, so that thefrit may be considered “on” a substrate even if other material (e.g., acoating and/or thin film) is provided between the substrate and thefrit.

In certain example embodiments of this invention, a method ofpreferential heating for frit edge seal of vacuum insulated glass unitsusing a unitized zoned oven is provided. The pre-assembled unit is firstheated to an intermediate temperature lower than that required to meltthe frit seal (e.g., a temperature of about 200-300° C.). Then, the edgeof the unit is further heated with localized heat from a substantiallylinear focused infrared (IR) heat source and/or via at least onesubstantially two-dimensional array of heat sources that is configuredto generate IR radiation at a near infrared wavelength (e.g., awavelength of about 0.7-5.0 μm) and, more preferably, of about 1.1-1.4μm, in order to provide a localized temperature of from about 350-500°C. until the frit is melted. At the same time, if tempered or heatstrengthened glass is used, at least certain portions of a thermallytempered glass sheet(s)/substrate(s) of the VIG unit lose no more thanabout 50% of original temper strength, as the majority of the area isstill under the intermediate temperature. Because of the overall lowertemperature, the techniques of certain example embodimentsadvantageously consume less energy and save time when the samples cooldown. It will be appreciated that the localized temperature may bedetermined based in part on the material(s) comprising the frit. Forexample, lead-inclusive frits tend to require lower temperatures thansilver-inclusive fits.

The unitized oven of certain example embodiments includes multiplechambers. Generally, the chambers will correspond to an entrance zone,an edge sealing zone, and an exit zone. It will be appreciated that anillustrative unitized oven may include multiple chambers foraccomplishing the functionality of a single zone (e.g., two entrancechambers may be provided for performing entrance zone functionality, twoexit chambers may be providing for performing exit zone functionality,etc.), and/or that a single chamber may be provided to accomplish thefunctionality associated with multiple zones (for example, a singlechamber may provide entrance and exit zone functionality, etc.).

By way of example and without limitation, FIG. 5 is a simplified sideview illustrating an example layout of a five chamber oven 50 inaccordance with an example embodiment. However, as alluded to above, itwill be appreciated that more or fewer chambers may be employed. Incertain non-limiting implementations, adjacent chambers may be separatedby sealing doors (represented by dashed lines in between adjacentchambers) located between them. Linkage, pulleys, and/or other means maybe provided to open and close such doors.

The unitized oven 50 of certain example embodiments is semi-continuousin terms of product flow. A roller conveyer 52 or other transporttechnique may be used to physically move a given VIG assembly from onezone and/or chamber to the next so that the VIG assembly and/or itscontents are not disturbed or repositioned relative to one another. At astart point 52 a, the roller conveyer 52 feeds VIG assemblies into theoven 50, e.g., through a first door 54. VIG assemblies may be moved intoplace and stopped when they reach a proper position within a chamberand/or zone. The position of the VIG assembly may be determined, forexample, by photo-eye or other detection means. By way of example andwithout limitation, the position may be the center of a particularchamber, aligned within particular horizontal and vertical positions(e.g., as described in greater detail below in relation to FIG. 6), etc.In certain example embodiments, it may be advantageous to temporarilystop a VIG assembly at a particular location, for example, to allow theVIG assembly to heat sufficiently, to allow a solder frit to melt, etc.

In certain example embodiments, multiple VIG assemblies may be fed intothe oven 50 at the same time so that they are processed in batch. Forexample, in a five-chamber oven like the one shown in FIG. 5, up to fiveVIG assemblies may be processed by the oven at a time, with the processbeing started and stopped in dependence on the progress of each chamber.For example, the edge sealing zone may require more time than thecooling performed in the exit zone chambers. Thus, there may be somedelay built into the process to account for the different process timesof the different zones and/or chambers.

The entrance zone (e.g., chambers 1 and 2 in the FIG. 5 exampleembodiment) is equipped with substantially uniform heat sources so thatthe VIG assembly is heatable in stages. That is, substantially uniformheat may be applied to the VIG assembly so as to substantially uniformlyheat the entire VIG assembly. Heating may be accomplished via IRradiation from an IR heat source or other means so as to reducedisturbance of the VIG assembly or its contents.

In an edge sealing zone (e.g., chamber 3 of FIG. 5), substantiallyuniform heating sources are installed to maintain the VIG assembly as awhole at a predetermined background temperature. This may beaccomplished by maintaining the entire VIG assembly at the intermediatetemperature from the entrance zone and/or slightly increasing thetemperature from the entrance zone. In the meantime, substantiallylinear focused IR heat sources 56 supply localized heating to theperimeter of the VIG assembly so as to melt the ceramic frit applied tothe edges. IR heat may be focused on peripheral edges, for example, bymeans of a parabolic mirror on an edge opposite to the VIG assembly.Further details of an example focusing mechanism are provided below withreference to FIG. 7. Although this particular zone is termed an edgesealing zone, it will be appreciated that some edge sealing may occur inother zones. For example, most melting will occur within the edgesealing zone and some edge sealing will take place once the IR radiationsources are powered down, although the edges may continue to seal (e.g.,the frit may begin or continue to harden) while in the exit zone.

FIG. 6 is an overhead view of the moving concentration of IR heatsources 62 and 64 in the edge sealing zone of a unitized oven inaccordance with an example embodiment. As shown in FIG. 6, the fritmelting oven is designed such that variously sized VIG assemblies may besealed. In certain example embodiments, one corner of the focused IRbank is fixed in position (e.g., the corner proximate to banks 62 a-b).In the FIG. 6 example, banks 62 a-b are fixed in position. In suchexample arrangements, only two sides of the focused IR bank would needto be repositioned to ensure proper frit melting. The IR sources alsomay be segmented into sections so that a part or all of the sections canbe turned on at any time to adjust the length of heating to that of theVIG assembly size. Parts of these IR source banks 64 a-b may be movedinto various positions around the perimeter of the VIG assembly bymechanical means, such as, for example, arms, rollers on a rail, and/orother linkages. In FIG. 6, this is shown as banks 64 a-b being segmentedand bank segments 64 a ′-b′ being moved from their initial positions(designated by the dotted lines in the banks 64 a-b) to positionsproximate to the VIG assembly 1′ (designated by the solid lines) to beedge sealed. In the FIG. 6 embodiment, only IR sources corresponding tobanks 64 a ′-b′ and parts of 62 a-b would be turned on; the rest of theIR sources in banks 64 a-b and the non-proximate IR sources in banks 62a-b need not be turned on (e.g., they would may remain off).

Thus, as is shown in FIG. 6, the localized heat source comprises first,second, third, and fourth banks of infrared heat source elements, thebanks being arranged such that the infrared heat source is substantiallyrectangularly shaped within the edge melting zone. The first and secondbanks are fixed in position and constitute two substantiallyperpendicular legs of the substantially rectangularly shaped infraredheat source, and the third and fourth banks constitute the other twosubstantially perpendicular legs of the substantially rectangularlyshaped infrared heat source. The infrared heat source elements of thesecond and third banks are movable in dependence on a size of the unitso as to move closer to the edges to be sealed.

In addition, the angle of the focusing mirror may be adjustable incertain example embodiments to allow the heat to be focused moreprecisely on the VIG assembly perimeters (as described in greater detailbelow with reference to FIG. 7). In certain example embodiments, the IRsegmented source movement and/or focusing may be computer-controlled toadjust the results of the individual units. Still further, the VIGassembly 1′ to be edge sealed may be elevated such that it is moreproximate to the IR sources. This may be accomplished by moving it intoa proper X-Y position with respect to the IR banks 62 a-b, movingportions of the movable IR banks 64 a-b, and lifting the VIG assembly I′into position.

By way of example and without limitation, the IR sources within thebanks may be IR tubes. The IR tubes may be close enough to each toprovide heating across the edges of the VIG assembly (e.g., withoutleaving “gaps,” or unheated or substantially differently heated areasaround the edges), but also may be far enough away from each other toallow for movement of such tubes. Thus, by way of example and withoutlimitation, the IR tubes may be located approximately 5 mm apart incertain example embodiments. The sizes of the banks may vary independence on the needs of the VIG unit manufacturing process. Also byway of example and without limitation, banks of about 2-3 meters shouldaccommodate most standard VIG unit manufacturing requirements.

Referring once again to FIG. 5, the VIG assembly may be cooled down inan exit zone comprising one or more chambers, e.g., in a stepwise mannervia chambers 4 and 5 of FIG. 5. When a stepwise exit zone arrangement isimplemented, each successive exit zone chamber may be maintained at alower temperature than the previous exit zone chamber. This arrangementmay be enabled by using forced convective air cooling, cooling waterpiping, and/or other cooling means suitable for removing heat from theparticular exit zone chamber. Ultimately, the VIG assembly may be rolledout of the oven 50 through exit door 58 via rollers 52 b.

FIG. 7 is a side view of a concentration and/or focusing mirror 72located proximate to an IR heating element 74 in accordance with anexample embodiment. It will be appreciated that any type ofconcentrating and/or focusing mechanism may be used in connection withcertain other example embodiments. IR radiation from IR heating element74 is focused and/or concentrated by the parabolic mirror 72 onto orproximate to solder frit 4. The mirror 72 may be moved and/orrepositioned to cause more or less of the peripheral edges of the VIGassembly 1′ to be heated, to focus IR radiation to or away from thesubstrates 2 and 3, etc.

A more detailed description of the VIG assembly edge sealing processwill now be provided. A pre-assembled VIG assembly, which may include apre-applied and fired perimeter frit ink, enters the oven. In theentrance zone, the VIG assembly is heated up to a predeterminedtemperature of between about 200-300° C. This may be accomplished usingstaged heating in one or more entrance chambers, so that the entire VIGassembly is pre-heated to one or more intermediate temperatures. Ingeneral, the VIG assembly will enter into the oven at room temperature(e.g., which typically is about 23° C., although it will be appreciatedthat other processing environments and/or conditions may implement adifferent “room temperature”). The entire VIG assembly may be heated toabout 75° C. in a first entrance zone chamber and then to about 150° C.in a second entrance zone chamber. It will be appreciated that thepre-heating temperatures may vary by about ±50° C.

In the edge sealing zone, the entire VIG assembly is heated to about200° C., and an IR heat source (e.g., a computer-controlledsubstantially linear IR heat source) is moved into position and focusedaround the perimeter of the VIG assembly. The IR heat source isactivated at a predetermined distance (e.g., from about 0.5-10 cm) fromthe edge of the VIG assembly, depending in part on thefocusing/concentrating mirror, whether the IR radiation is meant to“contact” the top and/or bottom substrates or just the sides proximateto the frit, etc. As noted above, the IR heat source is focused, e.g.,by means of a parabolic mirror provided on a side of the IR heat sourceopposite to the VIG assembly. The temperature of the frit on theperimeter of the VIG assembly is controlled to about 350-500° C., whichis suitable to melt the frit but still below the melting point of theglass substrates, which varies from about 600-800° C. based on thecomposition of the glass. During the localized heating process in theedge sealing zone, the glass temperature remains at the backgroundtemperature. Accordingly, heat strengthened or tempered glass, ifutilized, is not de-tempered or suffers a reduced amount of de-temperingduring the frit heating and/or melting processes.

Following the frit melting in the edge sealing zone, the VIG assembly istransported to the exit zone. The exit zone may include one or moretemperature ramp-down areas (or chambers). The temperature is reduced sothat the VIG assembly is at a temperature less than about 100° C. whenit exits the oven. In certain example embodiments, in a first exitchamber, the temperature of the entire VIG assembly will be reduced toabout 150° C. and then to about 75° C. in a second exit chamber. Asabove, ramp-down temperatures may vary from these figures by as much asabout ±50° C.

FIG. 8 is an illustrative flowchart showing a process for providinglocalized heating to frit edge seals of a VIG assembly via a unitizedoven, in accordance with an example embodiment. In step S82, a VIGassembly including a plurality of edges to be sealed is inserted into aunitized oven. A roller conveyer may convey the VIG assembly into theoven, e.g., through a door. In step S84, the VIG assembly is pre-heatedto one or more intermediate temperatures in an entrance zone of theunitized oven. The intermediate temperature(s) is/are below the meltingpoints of glass and the frit along the edge to be sealed.

Localized heat is provided to the edges of the VIG assembly to be sealed(e.g., using one or more substantially linear IR heat sources, producingIR radiation having a near infrared wavelength (e.g., a wavelength ofabout 0.7-5.0 μm) and, more preferably, of about 1.1-1.4 μm) in an edgesealing zone of the unitized oven in step S86. The localized heat is ata temperature above the intermediate temperature(s) and is sufficient tocause the frit around the edges to melt. The temperatures may be chosenin dependence on the composition of the frit material. The VIG assembly,apart from the areas proximate to the peripheral edges to be sealed, arekept at a temperature close to that of the intermediate temperature(e.g., at a temperature sufficiently low so as to avoid melting of theglass, not varying by more than about ±50° C. from an intermediatetemperature).

In a step not shown, to provide localized heating, a plurality of heatsources (e.g., substantially linear IR heat sources) are provided, e.g.,within a bank. At least some of the banks may be fixed in position. TheVIG assembly may be positioned proximate to the fixed banks so that atleast some of the edges to be sealed are adjacent to the fixed banks.Additional banks including movable heat sources may be positioned so asto provide heat proximate to the edges of the VIG assembly that are notadjacent to the fixed banks. The areas to be heated may be more finelytuned by providing a concentration and/or focusing mirror.

Referring once again to FIG. 8, in step S88, the VIG assembly is cooledin an exit zone of the oven. The pre-heating and/or cooling of the VIGassembly may be staged so as to reduce the chances of breakage of theVIG assembly and/or de-tempering of the substrates comprising the VIGassembly. In certain example embodiments, multiple chambers may beprovided for one or more of the zones. In connection with suchembodiments, multiple chambers may be provided for the ramping-up oftemperatures and/or the cooling processes, e.g., when the heating and/orcooling processes are staged. In certain other embodiments, a singlechamber may be configured to perform the functionality of multiple zones(e.g., a single chamber may pre-heat and/or cool the substrate, a singlechamber may pre-heat the substrate and/or provide localized heat to theedges, a single chamber may provide localized heat to the edges and/orcool the substrate, etc.).

Thus, certain example embodiments advantageously heat, melt, and coolthe frit quickly. This helps produce a temperature gradient proximate tothe edges of the VIG assembly. The temperature gradient, in turn, helpsreduce de-tempering and/or the chances of breakage of the glass. Incertain example embodiments, at least certain portions of a thermallytempered glass sheet(s)/substrate(s) of the VIG unit lose no more thanabout 50% of original temper strength.

Certain example embodiments provide heat to the edges of the VIG using alocalized heat comprising an array of focused IR heat sources so thatwhile the non-edge areas remain at relatively low temperature, the fritaround the perimeter is melted. The array of IR heat sources reduces thenumber of moving parts in the localized heating source and does notnecessarily require separation between temperature zones someembodiments. The array is installable into a standard belt furnacerelatively easily. Another advantage of this design is that it can beused to produce VIG units of various sizes and shapes (e.g.,substantially rectangular and substantially non-rectangular shaped VIGunits of varying sizes).

Instead of, or in addition to, implementing system of movable heatsources, certain example embodiments may provide localized heating by asubstantially stationary array of focused IR sources installed anin-line furnace, such as belt furnace or “coffin” style furnace. Thearray includes a matrix of W*L number of spot IR sources, each of whichcovers a fixed area. The On/Off behavior of the spot IR sources may beindividually controlled by a computer so that each spot on the edge willbe illuminated by the IR sources for a pre-determined fixed totalenergy, e.g., equal to the amount required to melt the frit. The widthof the array may cover the whole effective width of the belt, and thelength of the array may provide sufficient heating to melt the frit. Thelength of the array can be estimated by the equation:E=L*D/Vwhere E is the total energy per unit area used in melting the frit, L isthe length of the array, D is the power density of the IR source, and Vis the furnace line speed.

The operation of the array of IR sources will now be described ingreater detail with reference to FIGS. 9a-9f . For convenience, theindividual heat sources will be identified using a naming scheme whereeach individual source is designated as #LW, with the L- and W-axesbeing numbered as “1” at the intersection thereof shown in FIG. 9a .Thus, for example, in FIGS. 9a-9f , the upper-left heat source is #98,and the bottom-right heat source is #11.

FIG. 9a is an overhead view of the VIG assembly 1′ on a belt 92 in anoven prior to its entry under the IR source array 90, in accordance withan example embodiment. Before the VIG assembly 1′ goes under the IRsource array 90, all IR sources are turned off (e.g., as designated byall circles in the IR source array 90 being greyed-out).

FIG. 9b is an overhead view of the VIG assembly 1′ on a belt 92 in anoven entering into the IR source array 90, in accordance with an exampleembodiment. When the leading edge of the VIG assembly 1′ is under thearray, the IR sources covering the edge of the VIG assembly 1′ to besealed are turned on. Thus, in the FIG. 9b example, units #11 to #16 areturned on, as designated by the darkened circles. At this time, theother sources in the IR source array 90 remain off.

FIG. 9c is an overhead view of the VIG assembly 1′ further entering theIR source array 90 such that both the edge to be sealed along the minoraxis of the VIG assembly 1′ and portions of the edges to be sealed alongthe major axis of the VIG assembly 1′ are both exposed to IR from the IRsource array 90, in accordance with an example embodiment. As shown inFIG. 9c , the VIG assembly 1′ further enters the array region, and theIR sources switch from W=1 to W=2 and then to W=3 to follow the leadingedge. In the mean time, #11, #21, #16 and #26 remain “on” because theedges to be sealed along the major axis of the VIG assembly 1′ are to beexposed to heat.

FIG. 9d is an overview of the VIG assembly 1′ further entering the IRsource array 90 such that only the edges to be sealed along the majoraxis of the VIG assembly 1′ are exposed to IR from the IR source array90, in accordance with an example embodiment. Once only the side edgesare under the array, the “On” pattern becomes two parallel lines in themoving direction, and all other heat sources are turned “Off.” As shownin FIG. 9d , a second VIG assembly 1′ having edges to be sealed iscoming down the belt 92 towards the array.

FIG. 9e is an overhead view of the VIG assembly 1′ exiting the IR sourcearray 90, in accordance with an example embodiment. As the trailing edgeenters the array, the column L=1, 2, 3, . . . , will be turned on againin this order for the trailing edge. The whole column will be completelyoff after the trailing edge passes until the next assembly 1′ enters. Bythe time the VIG assembly 1′ leaves the array region 90, every spot onthe perimeter has received a substantially equal amount of energysufficient to melt the frit.

FIG. 9f is an overhead view of a second VIG assembly 1′ entering the IRsource array 90 as a first VIG assembly 1′ exits the IR source array 90in accordance with an example embodiment. As can be seen from FIG. 9f ,the first and second VIG assemblies 1′ are differently sized. Thus, whenthe second VIG assembly 1′ enters the array region, the process willrepeat, except that row W=7 will be on because of larger width for thesecond unit.

Thus, it will be appreciated that each heat source in each row andcolumn of the array is selectively activated in dependence on whether anedge to be sealed is proximate to the heat source (e.g., within an areaof heat produced by the heat source). It also will be appreciated thatthe array is substantially two-dimensional.

The determination of which sources to be turned on may be pre-programmedby an operator in certain example embodiments. In certain exampleembodiments, photo-eye or other detecting mechanisms may be used todetermine the size and/or position of the VIG assembly, e.g., todetermine the heat sources in the array to be turned on and the time atwhich they should be turned on.

It will be appreciated that the energy intensity produced by a single IRheat source (e.g., in an array) is substantially normally distributedacross an area such that the energy emitted is highest at the center ofthe area. Thus, an arrangement that incorporates an array ofspaced-apart IR heat sources may sometimes create “stripes” of high andlow energy areas. Sometimes, this may result in localized andnon-localized melting. That is, sometimes just enough or too much energywill be applied to a certain area or areas, while not enough energy willbe provided to an adjacent area or areas.

Accordingly, certain example embodiments may incorporate an array of IRheat sources where the heat sources are staggered. FIG. 10 is anoverhead view of an IR source array 90′ incorporating a staggered IRheat source design, in accordance with an example embodiment. In FIG.10, the individual heat sources in the array 90′ are arranged such that,moving left-to-right, the southeast section of the first heat source isadjacent to the northwest section of the second heat source, and thenortheast section of the second heat source is adjacent to the southwestsection of the third heat source, etc. This and/or other arrangementsmay advantageously help provide alternating high and low exposure areasto even out the striping that sometimes may otherwise occur. Thestaggered IR heat source design of FIG. 10 operates in substantially thesame was as the design of FIGS. 9a -9 f.

In certain example embodiments, diffusers may be placed proximate toeach lamp so as to even out the energy, which otherwise sometimes mightbe provided according to a particular shape (e.g., circular shape wherecircular lamps are used) or in stripes as noted above, thus providing asubstantially uniform distribution of heat across the area to be heated.Generally, a diffuser may be provided to each heat source in the arrayto provide a more uniform heat flux from the heat sources in the array.It will be appreciated that diffusers may be used in connection witheither the array design of FIGS. 9a-9f and/or the array design of FIG.10.

FIG. 11a is a side view of an in-line style belt furnace installed withan array 90 of IR sources. Pre-assembled VIG assemblies 1′ enter thefurnace and are heated up through a temperature ramp-up zone to reachthe predetermined background temperature (typically between about200-300° C.). An IR array 90 is installed in this background temperaturezone and melts the frit around the perimeter of the VIG assemblies 1′ ina process described above or other process. During the whole time, thefurnace belt 92 may be moving continuously at a constant speed selectedto provide sufficient heating to the perimeters of the VIG assemblies 1′to ensure good hermetic seals around the edges of the VIG assemblies 1′.The pumping port tube seal, if necessary, can also be sealed in the sameor other fashion using the IR array 90 at the same time. The individualIR heat sources are switched on and off by computer-control to provideadequate preferential heating to the edges of the VIG assemblies 1′. Thetemperature of the frit on the edge of the VIG assemblies 1′ iscontrolled between about 350-500° C., suitable to melt frit but belowglass melting point. In the meantime, the glass temperature remains ator close to the background temperature. The VIG assembly 1′ is thentransported through temperature ramp down zones until it cools down,e.g., to less than about 100° C. when it exits the oven. As noted above,the zones may be separate chambers or they may be the same chambers incertain example embodiments.

It will be appreciated that when turning on a single IR heat source, theenergy produced is substantially normally distributed over time. Thus,the energy will often ramp-up, stabilize, and then ramp-down.Accordingly, in certain example embodiments, a computer-controlledsystem may advantageously turn on a single lamp before the VIG assemblyis underneath it to ensure that the intended energy reaches the area,and/or also turn off the lamp before the VIG assembly exits to reducethe exposure to adjacent areas that should not be heated. Thus, as theunit moves across successive columns of the array, each heat source isactivated in the row and column of the array before the edge to besealed is exposed to heat emanating from the heat source and alsodeactivated before the edge to be sealed is removed from the heatemanating from the heat source.

FIG. 11b is a side view of an in-line style belt furnace installed withtwo arrays 90 of IR sources in accordance with an example embodiment.For example, an additional array may be provided between the belt andpoint upward so that the two arrays heat the edges to be sealed fromboth sides. That is, heat may be applied to both sides of the frit toensure faster and/or more uniform melting thereof. The two arrays 90 maybe controlled in the same way by the same or different means to ensurethat the edges become sealed. Alternatively, a slight delay betweenon-off cycles or slightly different on-off configuration may beintroduced between arrays, e.g., to help reduce the striping problemdescribed above.

The above-described and/or other example embodiments may involve atunable IR heat source operable to impart a substantial portion ofenergy in that wavelength range. The IR heat source may be used toselectively heat an applied material such as, for example, a film,application, paint, solder glass, metal, metal and/or ceramic coating,bead, profile, etc., that has been applied to a glass or ceramicsubstrate surface to a prescribed temperature, thereby causing a desiredphysical and/or chemical change (such as, for example, melting,sintering, chemical property change, outgassing, etc.).

In certain example embodiments, an arrangement of heating elements isprovided in a configuration that imparts localized or diffuse energytransfer to an area of interest. In certain example embodiments, IRbulbs may be designed to create a predetermined spectral response. TheIR bulbs may be further fine-tuned via voltage adjustments. Thus, it maybe possible to produce a desired peak wavelength, e.g., by providingbulbs that create an approximate spectral response and by providingvoltage adjustments to further fine-tune at least the peakwavelength(s). This approach is advantageous in certain exampleimplementations, as voltage changes may be finely controlled, e.g., insmall increments, thereby resulting in smaller overall powerconsumption, a reduced amount of electrical stress on the system, etc.

The bulbs may be made to emit a certain peak wavelength if theirelements (e.g., tungsten or other elements) are adjusted in terms ofdistance and/or cross-sectional area. These dimensional changes may helpto change the resistance and thus the heat produced and, in turn,affecting the spectrum of the emitted energy. As alluded to above, IRlight in the near infrared (NIR) and/or short-wave infrared (SWIR) bandsmay be used. Such spectra commonly encompass wavelengths of, forexample, 750-1400 nm and 1400-3000 nm, respectively. Some frits usablein VIG applications may be tuned to absorb energy in this range. It alsois possible to tune such frit materials (e.g., through the use ofpigments and/or additives) such that it has a relatively flat absorptionacross a spectrum where the glass substrate that supports it has arelatively low absorption. Thus, in certain example embodiments, theelements may be tuned away from wavelength ranges of high absorption forthe glass, and towards wavelength ranges of high or peak absorption forthe frit. In certain example embodiments, wavelengths of from about1300-1700 nm have been found to be advantageous in that frit materialsare highly absorptive in this area, whereas absorption by the glass isrelatively low. As indicated above, these elements may be further tunedby changing the voltage so as to control the frequency at which theyemit the most energy.

FIG. 12 is a graph that plots transmission, reflection, and absorptionvs. wavelength for an example glass frit. As can be seen, the frit isoptimized for heating via an IR wavelength of 1300-1700 nm. In certainexample embodiments, the frit material may be a vanadium-based fritmaterial. See, for example, application Ser. No. 12/929,875, entitled“VANADIUM-BASED FRIT MATERIALS, AND/OR METHODS OF MAKING THE SAME”, theentire contents of which are incorporated herein by reference. Other fitmaterials may be used including, for example, Ferro 2824B and 2824Gfrits. See, for example, application Ser. No. 12/929,874, entitled“IMPROVED FRIT MATERIALS AND/OR METHOD OF MAKING VACUUM INSULATING GLASSUNITS INCLUDING THE SAME”. Other so-called “lead-free” frits may be usedin different embodiments.

FIG. 13 is a graph showing glass absorption vs. wavelength for 3.2 mmclear float glass. FIG. 13 also shows example profiles for tungstenelement outputs operating at different peak wavelengths. As can beensee, glass absorption increases gradually until just over 2.5 micronwavelengths, where the jump is approximately vertical. Thus, it isdesirable to tune the IR heating elements (and the IR frit compositions)towards the NIR and/or SWIR bands and, for example, to peaks around 1.14or 1.30 microns, where IR absorption is relatively is comparatively low.In certain example embodiments, the frit is tuned to a wavelength suchthat it absorbs at least about twice as much heat from the IR elementscompared to the glass substrate, more preferably at least about threetimes as much heat, and still more preferably 3.5 or more times as muchheat.

FIG. 14 correlates voltage with temperature for example IR heatingelements. As can be seen, the higher the voltage, the lower thetemperature. It also can be seen that the glass remains at a temperaturelower than the frit for all voltages. As will be appreciated, a highglass/frit temperature difference is desirable in certain exampleembodiments. And as explained above, this may be accomplished by tuningthe peak output from the IR heating element(s) towards the fries rangeof absorption and away from the glass's range of absorption.

The distance between the element and the part to be heated also may beadjusted so as to control the energy flux, e.g., in adjusting theheating profile. In other words, in certain example embodiments, it ispossible to adjust the vertical distance between the IR emitters and thepart to be heated. Jack screws or the like may be used to accomplishsuch movement. The movement may be manual or automatic in certainexample embodiments. It will be appreciated that in certain exampleembodiments, the IR emitters may be provided in a fixed verticalposition relative to the part to be heated. In general, a distance ofabout 2-10″, more preferably 3-6″, and sometimes about 4″ from the topof the glass of a VIG unit may be desirable.

The energy flux also may be adjusted by changing the distance betweenadjacent heating elements. In certain example implementations, a 2-6″(and sometimes 4″) center-to-center distance may be provided foradjacent bulbs. It has been found that this example center-to-centerdistance is advantageous in that an appropriate amount of heat isproduced. Placing the bulbs too close together may produce too much heatfor the frit material and/or the substrates.

The emitters may be provided at different angles relative to the targetarea to be heated in different embodiments of this invention. Forinstance, in an example stationary oven where items are simply insertedor removed, an approximately 90 degree bulb angle (e.g., ±15 degrees)relative to the surface on which they are mounted (e.g., a surfacedirectly above the part to be heated) was found to be advantageous interms of producing a desired heating profile. By contrast, in an exampleoven where products moved in and out on a roller-based conveyor system,approximately 45 degree angles (e.g., ±15 degrees) for the bulbs werefound to be advantageous in terms of producing a desired heatingprofile. That is, certain example embodiments may use generally elongatebulbs that are generally horizontally oriented with a chamber, and withthose bulbs being generally perpendicular to or angled towards/away fromupper and/or lower surfaces of the VIG subassembly. In certain exampleembodiments, the bulbs may be provided above and/or below the VIGsubassembly.

In certain example embodiments, one or more backing or other mirrors maybe used to help focus heat generated by the IR element(s).

The heating elements themselves may be cooled by convective, conductive,and/or other cooling means in certain example embodiments.

The applied material to be heated (e.g., the frit slurry that mayinclude ceramic materials, a water or other solvent base vehicle andbinder; paint; a coating; solder glass; metals; metallic and/orsemiconductor coatings including, for example, pyrolytic or sputteredfilms; etc.) may absorb energy and heat up at a faster rate than theglass or ceramic substrate by which it is supported. This selectiveheating is advantageous in that the heat has a reduced effect on thesubstrate properties, e.g., as related to the lower buildup of heatcompared to the applied material. Thus, it will be appreciated that ifthe substrate is heat treated (e.g., heat strengthened or temperedglass), the bulk properties may be largely unchanged, given that thefrequency at which energy is imparted to the part is targeted at theapplied material rather than the glass substrate.

FIG. 15 is a graph with absorption properties of a frit materialaccording to certain example embodiments. The illustrative graph showsabsorption percentage versus wavelength in nanometers. Two differentfrit materials are shown, frit 1 and frit 2. Frit 1 is an improved fritmaterial according to certain example embodiments of application Ser.No. 12/929,874, the entire contents of which are hereby incorporatedherein by reference, and frit 2 is a conventional frit material. Alsoshown are two different types of glass. The first is a conventionalclear float glass. The second (RLE-coated glass) is a coated glasssubstrate, although it will be appreciated that different exampleembodiments may use different low-E coatings. As can be seen from thegraph, frit 1 includes increased absorption properties versus frit 2.Indeed, frit 1 maintains an absorption percentage above 80% for thelength of the illustrated graph and at or near 90% for a substantialportion of the graph. Conversely, frit 2 has a maximum absorption in the300 nm wavelength range and subsequently drops off quickly untilmaintaining about 20% absorption in the medium to long wave length IRregions.

As shown, frit 2 possesses absorption properties similar to those foundin the glass substrates. Accordingly, when frit 2 is disposed on suchglass substrates, both the glass and the frit may absorb similar amountsof IR energy. The similar absorption properties of the IR energy maylead to both the frit and the glass substrates having similar heatingprofiles. In contrast, the absorption properties of frit 1 provide asubstantially increased ability to absorb IR energy. Accordingly, incertain example embodiments, a frit material with a high IR absorptionpercentage may be provided, for example above about 80%, or preferablyabove 85%, and even more preferably above about 90%, for at least asubstantial portion of the IR wavelengths in question. It will beappreciated, of course, that a frit material having 50% or 75% IRabsorption also is possible in certain example implementations.

Although the selective or preferential heating of an area isadvantageous, the inventors of the instant application have alsoobserved that the heating profile of the article as a whole matters. Asindicated above, de-tempering is a risk for monolithic articles.However, the inventors of the instant application have observed that therisk is heightened for VIG units. In other words, substrates used in VIGunits are more sensitive to de-tempering than their monolithic glasssubstrate counterparts. Thus, certain example embodiments help ensurethat substrate temperature preferably is no higher than 375 degrees C.for 1 minute, more preferably no higher than 350 degrees C. for 1minute, and still more preferably no higher than 325 degrees C. for 1minute.

In addition, a uniform temperature control across the glass substrate asa whole also impacts the end performance. Thus, uniformity of heatingacross frit and the substrate is desirable. Such uniformity isadvantageous in helping to avoid the creation of “hot spots” or areas oflocalized over-heating. Such hot spots may cause de-tempering of theglass substrates, the formation of bubbles or air pockets in the frit,the over-firing of the frit, etc. Preferably, the substrate surfaceand/or frit has a temperature that differs by no more than ±5 degreesC., more preferably by no more than ±2 degrees.

It has been found that the inner surfaces of the chamber used for IRheating can cause reflections of the IR beams. These reflections alsomay cause “hot spots,” potentially in or on the frit and/or substrate,and thus may reduce the overall temperature uniformity within thechamber and/or on the substrates. Certain example embodiments thus helpcontrol the temperature of the glass and the frit by creating a diffusepattern of energy by altering the surface characteristics of certainsurfaces within the chamber. The changes to these surfaces also may helpreduce the impact of reflections off of the glass surfaces.

More particularly, certain example embodiments may incorporate “hazy”inner wall surfaces that helps reduce directed reflections and/or helpscreate a more diffuse pattern of reflections. This may be accomplishedby providing an inner wall of a hardened high temperature resistant battmaterial, rather than a more “shiny” (and thus reflective) metalmaterial. In certain example embodiments, the batt material may be ahigh-temperature silica-based rock wool or like material. The hardenedbatt material has a higher haze and thus helps to create a more diffusepattern of radiation which, in turn, leads to more uniformity inheating. Further insulation may be provided around the inner batt walls.In certain example embodiments, the inner wall material may have lowreflectivity in at least the IR range, e.g., less than 50%, morepreferably less than 25%, still more preferably less than 20%, possiblyless than 10-15%, and sometimes even lower. In such cases, the reducedamount of IR may be reflected in a diffuse pattern.

Preheating may be provided in certain example embodiments by virtue ofconvection or other heating means, although certain example embodimentsdo not involve preheating. Instead, the chamber may be kept at anelevated temperature (e.g., of 100 degrees C.) and some or all of theglass may be heated by the IR heating element(s) alone. In such cases,the IR heating element(s) may be operated at 50% voltage for pre-heatingsome or all of the glass and/or for maintaining the elevated (e.g., 100degree C.) temperature, whereas an increased 70-80% voltage may beprovided for the actual sealing process. In certain example embodiments,50% and 80% voltages may be provided for these two modes, although thevoltage may vary somewhat, e.g., preferably ±10%, more preferably ±5%.As shown in detail below, the 50% and 80% voltages are surprising andunexpected.

As alluded to above, the density of IR irradiation was a large factor incausing detempering. In sum, the use of full lamps to produce shortrecipe times resulted in almost complete detempering of the VIG, whereasthe use of half bulb power density (50% bulb usage) retained temper thebest for both coated and clear glass and almost equal breakage.Surprisingly and unexpectedly, IR voltage at half bulb density (50% bulbusage) had the best temper retention at 50% and 80%. The other voltagesresulted in greater temper loss based on breakage patterns.

Thermal profiles were developed using the following techniques:

-   1. Started at 100 degrees C. using convection heat to warm the    glass.-   2. The convection fan was turned off. The glass was allowed to    stabilize for 2-3 minutes. This reduced the temperature    non-uniformity from the convection air flow issues with the SWIR.-   3. The time and IR voltage was adjusted to provide 3 minute heat up    to 275 degrees C. and then hold for 3 minutes to allow glass/frit to    stabilize to 275 degrees C.-   4. A ramp based on the voltage matrix targeted 350 degrees C. peak    temperature, for a full bulb (100% bulb usage) at 40%, 50%, and 60%    voltages, and for half bulbs (50% bulb usage) at 50%, 60%, 70%, 80%,    90% voltages.-   5. IR voltage adjusted to hold for 1 minute at 350 degrees C.    temperature.-   6. The cool down had maximum air injected 30 seconds after IR was    reduced. This increased the oven and glass cool down to minimize the    effect of heat on detempering.

The 19 thermocouple system was used to measure the temperature. The IRvoltage was adjusted accordingly to obtain best possible temperatureuniformity. Approximately 10 degrees C. (±5 degrees C.) uniformity wasobtained for the ramp up and peak hold.

After all the profiles were completed, each was run with coated(78/31)/clear 14×20 standard tempered glass mated together (no frit). Itwill be appreciated, however, that different example embodiments mayincorporate different heat treatable and/or other double-, triple-, orquad-silver based coatings. Breaks were done with spring punch, 1 inchinboard in the middle of the long perimeter.

Cool down of the oven was found to be a significant source of breakage.Accordingly, certain example embodiments may include air pipes installedinto the oven. In certain example implementations, 70-80 cfm of air maybe provided to the oven when the valve is on, thereby helping to removesome of the heat generated during ramp-up and also helping to morequickly cool the glass.

As indicated above, certain example embodiments do not requireconvection heat during ramp-up and, instead, only IR heating is used.The example technique of allowing the glass to reach 100 degrees C. andthen turning off the heaters and fan allows the elements to be coolerand have less latent heat left during the cool down process. Thus, thesetechniques may in certain example instances help reduce the heat loadfrom the oven mass and heating elements so there is a lower total amountof heat to extract during cool down.

The following table summaries the breakage per the voltage and bulbparameters, and the actual recipes and thermal profiles are providedbelow.

Bulb IR Voltage Density Setup Coated Std Temper Clear Std Temper Full40% Totally detempered Severely detempered Full 50% Totally detemperedSeverely detempered, best of the full IR Full 60% Totally detemperedSeverely detempered Half 50% Smallest breaks, Smallest breaks, good goodHalf 60% Moderately detem- Moderately detem- pered pered Half 70%Moderately detem- Moderately detem- pered better than pered better than60% 60% Half 80% Small breaks, almost Small breaks, almost as good as50% half as good as 50% half bulb bulb Half 90% Most detempered of Mostdetempered of half bulb series half bulb series

Given this example data, several observations may be made in terms of IRvoltage and density based on “equal” thermal profiles. The full bulbs(100% bulb usage) caused severe detempering in both lites, with thecoated articles being most effected (completely detempered). The halfbulbs (50% bulb usage) had a more equal impact on both coated and clearproducts and had less of a detempering effect.

In general, the half bulbs (50% bulb usage) had two best temper breakageregions, at voltage of 50% and 80%. The half bulb density (50% bulbusage) involves 2,000 watt bulbs spaced 4 inches apart, with a distanceof the glass to the bulb of 4 inches. In certain example embodiments, itmay be advantageous to avoid significant overlaps of IR energy from theIR bulbs. The temper breakage for all trials showed a good uniformity ofbreakage across the 14×20 sheets, indicating adequate temperatureuniformity for uniform heating/cooling.

The following table identifies example heating profile steps andtemperature measurements for those steps with a 40% voltage, full bulb(100% bulb usage) trial. This information is shown visually in FIGS.16a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 100 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 3.6 0 40 2240 37 23 32 0 0 Hold 3.0 0 15 8 23 30 7 21 0 0 Ramp 3.2 0 37 16 38 41 1535 0 0 off 0.1 0 5 5 5 5 5 5 0 0 on 0.5 0 30 17 30 30 17 30 0 0 off 0.10 5 5 5 5 5 5 0 0 on 0.5 0 30 17 30 30 17 30 0 0 cool 2.0 0 10 0 5 5 0 50 100 cool 15.0 0 10 0 5 15 0 5 50 100 end Half 1.0 0 0 0 0 0 0 0 0 100IR

The following table identifies example heating profile steps andtemperature measurements for those steps with a 50% voltage, full bulb(100% bulb usage) trial. This information is shown visually in FIGS.17a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 100 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 3.6 0 40 2240 37 23 32 0 0 Hold 3.0 0 15 8 23 30 7 21 0 0 Ramp 1.8 0 45 23 50 50 2250 0 0 off 0.1 0 5 5 5 5 5 5 0 0 on 0.5 0 30 17 30 30 17 30 0 0 off 0.10 5 5 5 5 5 5 0 0 on 0.5 0 30 17 30 30 17 30 0 0 cool 2.0 0 10 0 5 5 0 50 100 cool 15.0 0 10 0 5 15 0 5 50 100 end Half 1.0 0 0 0 0 0 0 0 0 100IR

The following table identifies example heating profile steps andtemperature measurements for those steps with a 60% voltage, full bulb(100% bulb usage) trial. This information is shown visually in FIGS.18a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Temp Front MiddleBack Front Middle Back % % (min) C. 275 Glass at 100 C., use 10% or 25%IR to obtain, then off 2-3 min to stabilize 3.6 0 40 22 40 37 23 32 0 03.0 0 15 8 23 30 7 21 0 0 1.2 0 60 40 60 60 40 60 0 0 0.1 0 5 5 5 5 5 50 0 0.5 0 30 17 30 30 17 30 0 0 0.1 0 5 5 5 5 5 5 0 0 0.5 0 30 17 30 3017 30 0 0 2.0 0 10 0 5 5 0 5 0 100 15.0 0 10 0 5 15 0 5 50 100 1.0 0 0 00 0 0 0 0 100

The following table identifies example heating profile steps andtemperature measurements for those steps with a 50% voltage, half bulb(50% bulb usage) trial. This information is shown visually in FIGS.19a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 100 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 5.0 0 50 3560 59 30 50 0 0 Hold 3.0 0 32 15 43 40 9 33 0 0 Ramp 9.0 0 40 15 50 5020 50 0 0 off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 50 30 50 50 30 50 0 0off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 50 30 50 50 30 50 0 0 cool 2.00 20 0 5 15 0 5 0 100 cool 15.0 0 5 0 5 5 0 5 50 100 end Half 1.0 0 0 00 0 0 0 0 100 IR

The following table identifies example heating profile steps andtemperature measurements for those steps with a 60% voltage, half bulb(50% bulb usage) trial. This information is shown visually in FIGS.20a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 275 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 5.0 0 50 3560 59 30 50 0 0 Hold 3.0 0 32 15 43 40 9 33 0 0 Ramp 4.0 0 56 34 63 6031 62 0 0 off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 50 30 50 50 30 50 0 0off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 50 30 50 50 30 50 0 0 cool 2.00 20 0 5 15 0 5 0 100 cool 15.0 0 5 0 5 5 0 5 50 100 end Half 1.0 0 0 00 0 0 0 0 100 IR

The following table identifies example heating profile steps andtemperature measurements for those steps with a 70% voltage, half bulb(50% bulb usage) trial. This information is shown visually in FIGS.21a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 275 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 5.0 0 50 3560 59 30 50 0 0 Hold 3.0 0 32 15 43 40 9 33 0 0 Ramp 2.5 0 66 40 74 7040 70 0 0 off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 60 40 60 60 40 60 0 0off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 60 40 60 60 40 60 0 0 cool 2.00 20 0 5 15 0 5 0 100 cool 15.0 0 5 0 5 5 0 5 50 100 end Half 1.0 0 0 00 0 0 0 0 100 IR

The following table identifies example heating profile steps andtemperature measurements for those steps with an 80% voltage, half bulb(50% bulb usage) trial. This information is shown visually in FIGS.22a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 275 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 5.0 0 50 3560 59 30 50 0 0 Hold 3.0 0 32 15 43 40 9 33 0 0 Ramp 1.8 0 76 50 83 7848 80 0 0 off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 60 40 60 60 40 60 0 0off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 60 40 60 60 40 60 0 0 cool 2.00 20 0 5 15 0 5 0 100 cool 15.0 0 5 0 5 5 0 5 50 100 end Half 1.0 0 0 00 0 0 0 0 100 IR

The following table identifies example heating profile steps andtemperature measurements for those steps with a 90% voltage, half bulb(50% bulb usage) trial. This information is shown visually in FIGS.23a-b , which plot temperature vs. time for top and bottom locations,respectively.

Duct Top Top Top Bottom Bottom Bottom Fan Damper Step Step Temp FrontMiddle Back Front Middle Back % % ID (min) C. 100 Glass at 100 C., use10% or 25% IR to obtain, then off 2-3 min to stabilize Ramp 5.0 0 50 3560 59 30 50 0 0 Hold 3.0 0 32 15 43 40 9 33 0 0 Ramp 1.4 0 85 60 96 9060 90 0 0 off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 50 30 50 50 30 50 0 0off 0.1 0 10 10 10 10 10 10 0 0 on 0.5 0 50 30 50 50 30 50 0 0 cool 2.00 20 0 5 15 0 5 0 100 cool 15.0 0 5 0 5 5 0 5 50 100 end Half 1.0 0 0 00 0 0 0 0 100 IR

It will be appreciated that the example profiles described above involveno cycling on-and-off of the bulbs, e.g., based on position of the VIGsubassembly relative to the bulbs. Rather, in certain exampleembodiments, the bulbs may be controlled solely based on temperaturerequirements.

Certain example embodiments have been described as relating to half bulbdensity (or 50% bulb usage) and full bulb density (or 100% bulb usage).It will be appreciated that this refers to the approximate number ofbulbs in an array of bulbs that are turned on or off. That is, half bulbdensity (or 50% bulb usage) refers to approximately one-half of thebulbs being on with the rest being off, etc. In such a scenario, everyother bulb may be on, etc., although other arrangements are possible indifferent implementations. Bulbs suitable for use in certain exampleimplementations include those commercially provided by Castle Solar.

It will be appreciated that the example embodiments described herein maybe used in connection with a variety of different VIG assembly and/orother units or components. For example, the substrates may be glasssubstrates, heat strengthened substrates, tempered substrates, etc.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of making a vacuum insulated glass (VIG)unit comprising an edge seal, the method comprising: inserting asubassembly for a VIG unit including first and second glass substrateswith seal material comprising frit therebetween into an apparatusincluding: a plurality of infrared (IR) heating elements that comprisebulbs controllable to emit IR radiation at a peak wavelength in the nearinfrared (NIR) and/or short wave infrared (SWIR) band(s), the pluralityof IR heating elements being spaced apart from one another so as to havea 2-6″ center-to-center distance and being vertically positioned 2-10″above an upper surface and/or below a lower surface of the VIGsubassembly, heating frit of the seal material provided proximate theperiphery of the subassembly via the plurality of IR heating elements informing the edge seal, the amount of voltage being supplied to theplurality of IR heating elements being adjustable to vary the peakwavelength produced by the plurality of IR heating elements so as topreferentially heat the frit compared to glass substrates of the VIGsubassembly, and during said heating when approximately half of thebulbs are in an “on” state for heating the seal material, approximatelythe other half of the bulbs are in an “off” state so that approximatelyhalf bulb density is employed during said heating.
 2. The method ofclaim 1, wherein the peak wavelength is between 1300-1700 nm.
 3. Themethod of claim 1, wherein the peak wavelength is selected so that atleast about three times as much energy is absorbable by the frit ascompared to glass substrates of the subassembly.
 4. The method of claim1, wherein the IR heating elements are oriented at approximately 90degree angles relative to a surface on which they are mounted.
 5. Themethod of claim 1, wherein the IR heating elements are oriented atapproximately 45 degree angles relative to a surface on which they aremounted.
 6. The method of claim 1, maintaining a stable heatingenvironment in which the temperature across the subassembly varies by nomore than ±5degrees C.
 7. The method of claim 1, further comprisingmaintaining an interior of the apparatus at a first elevated temperaturevia the IR heat elements and without the use of any further heatingelements, the first elevated temperature being lower than a temperatureneeded to form the edge seal.
 8. The method of claim 7, furthercomprising adjusting the output of the TR heating elements via voltagechanges to move from the first elevated temperature to the temperatureneeded to form the edge seal once the subassembly has been inserted intothe apparatus.
 9. The method of claim 1, wherein glass substrates of thesubassembly do not reach a temperature of 325 degrees C. for longer than1 minute during the heating of the frit material.
 10. A method of makinga vacuum insulated glass (VIG) unit comprising an edge seal, the methodcomprising: providing a subassembly for a VIG unit in an apparatusincluding at least one heating area, the subassembly for the VIG unitincluding first and second tempered glass substrates with spacers, a gapand seal material comprising frit located at least partially between theglass substrates, wherein a periphery of the gap is defined by the sealmaterial; the apparatus including a plurality of infrared (IR) heatingelements that comprise bulbs which are controllable to emit IR radiationat a peak wavelength in the near infrared (NIR) and/or short waveinfrared (SWIR) band(s), heating frit of the seal material providedproximate the periphery of the subassembly via the plurality of IRheating elements in forming the edge seal so as to preferentially heatthe frit compared to glass substrates of the VIG subassembly, and duringsaid heating when approximately half of the bulbs in the heating areaare in an “on” state for heating the seal material, approximately theother half of the bulbs in the heating area are in an “off” state sothat approximately half bulb density is employed during said heating.11. The method of claim 10, wherein the peak wavelength is between1300-1700 nm.
 12. The method of claim 10, wherein the peak wavelength isselected so that at least about three times as much energy is absorbableby the frit as compared to glass substrates of the subassembly.
 13. Themethod of claim 10, further comprising adjusting voltage provided to thebulbs in order to adjust the peak wavelength(s).
 14. The method of claim10, further comprising evacuating the gap to a pressure less thanatmospheric pressure after said heating.
 15. A method of making a vacuuminsulated glass (VIG) unit comprising an edge seal, the methodcomprising: providing a subassembly for a VIG unit in an apparatusincluding at least one heating area, the subassembly for the VIG unitincluding first and second glass substrates with spacers, a gap and sealmaterial comprising frit located at least partially between the glasssubstrates, wherein a periphery of the gap is defined by the sealmaterial; the apparatus including a plurality of infrared (IR) heatingelements which are controllable to emit IR radiation at a peakwavelength in the near infrared (NIR) and/or short wave infrared (SWIR)band(s), heating frit of the seal material provided proximate theperiphery of the subassembly via the plurality of IR heating elements informing the edge seal so as to preferentially heat the frit compared toglass substrates of the VIG subassembly, during said heating when afirst portion of the IR heating elements in the heating area are in an“on” state for heating the seal material approximately the remainder ofthe IR heating elements in the heating area are in an “off” state sothat only partial IR heating element density is employed during saidheating; and wherein glass substrates of the subassembly do not reach atemperature of 325 degrees C. for longer than 1 minute during theheating of the frit material.